Field of the Invention
The invention relates to a device for adjusting the position of sheet material when a direction of motion thereof is reversed, for example when sheet material is turned or reversed between printing units in multi-color rotary printing machines.
The published German Patent Document DE 41 13 478 A1 is concerned with an electronic sheet inspection device for cylinders in sheet-fed rotary printing machines. Sensing elements including linear CCDs and a light source register the leading edge of the respective sheet-material and the correct position thereof for a register-maintaining sheet transfer. By this inspection device, curved regions of a sheet-material leading edge are detected, in order specifically to correct possible faults by changing printing parameters. This paper position inspection makes it possible to register the sheet leading edge in the gripper system of each printing unit in a printing machine, in order even to detect printed sheet positional changes in the gripper system during the sheet transfer from one cylinder to another cylinder. The determined measured values are fed out of the cylinder to an evaluation device and are held ready in a data storage device for interrogation when the cylinder is at a standstill.
The published German Patent Document DE 85 03 577 U1 describes a register rail or bar having rotatably motor-driven setting screws, for stopping the leading edge of a respective sheet. By the rotatably motor-driven setting screws, the register rail or bar can be given a slight curvature, in order to bow the sheet slightly during the sheet acceleration in order to improve the contact thereof with the outer cylindrical or jacket surface of a cylinder.
The published German Patent Document DE 44 06 740 A1 discloses a device for color register correction in a rotary printing machine. In this correction device, a sheet holder grips the sheet at an edge region thereof leading in the conveying direction, electronic measuring elements being provided for establishing the sheet position. Sheet holders are displaceably arranged and are connected to motorized actuating elements controlled by the measuring elements. According to this embodiment, the sheet holders are constructed so as to be movable in the conveying direction and transversely to the conveying direction of the sheet. Signals from a nominal/actual comparison of the measuring elements determining the sheet position control the associated actuating elements which influence the sheet position at a contact surface.
It has become known heretofore that the color register of sheet material to be reversed or turned is always determined by the position of the leading edge of the sheet material. The trailing edge of the sheet material cannot be used as a reference edge, because of cut tolerances on the printing materials, which occur during the production thereof. A precondition for a good color register, i.e., one which maintains tolerance, is the maintenance of tolerance of the transfer color register. This means that the leading edge of each individual copy of the sheet material is positioned within the transfer color register tolerance range in the gripper system of a storage drum or a machine component, for example, which is the last to carry the printing material at the leading edge thereof before the printing material is picked up at the trailing edge thereof. In order to achieve this, the sheet is tautened in various ways at the trailing edge on the outer cylindrical or jacket surface of a sheet-carrying cylinder. For this purpose, use is made, for example, of sucker systems, which are capable of performing a relative movement with respect to the circumferential direction of the respective sheet-carrying cylinder, and exert a pulling force on the copy of the sheet material. The respective gripped copy is completely smoothened thereby, i.e., tautened, before the printing material is transferred to a gripper system for fixing the printing-material trailing edge.
The quality of the tautening of the sheet material on the outer jacket surface of the sheet-carrying cylinder, respectively, carrying the sheet material controls the manner in which the perfecting register, i.e., the systematic deviation of each piece of sheet material from the nominal or desired position, results in each case, taking into account tautening faults which are always the same from sheet to sheet, and/or the perfecting register, i.e., a stochastic deviation from the nominal position, for example, of tautening faults which repeatedly occur irregularly from sheet to sheet. These printing quality criteria are always determined in the same way by the relative position of the tautening elements, for example, tautening elements which are displaceable from the circumferential direction thereof on the outer jacket surface, to the gripper system for fixing the trailing edge of the fixed sheet material. In this regard, the perfecting register is determined by the accuracy; the color register is determined by the precision of repetition. Both operations, and particularly the tautening operation, cannot be performed with the demanded precision at higher printing speeds and in the case of certain printing materials, so that this circumstance has to be taken into account when turning or reversing sheet material between printing units of rotary printing machines.
In view of the afore-discussed prior art and the aforementioned technical problem, it is an object of the invention to provide a device for adjusting the position of sheet material when a direction of motion thereof is reversed, wherein turned or reversed sheet material is optimally adjusted in the position thereof even during the turning or reversing operation.
With the foregoing and other objects in view, there is provided, in accordance with a first aspect of the invention, a method of correcting a position of sheet material on conveying elements, the sheet material extending from a surface of a first sheet-conveying element to a surface of a second sheet-conveying element following downline from the first sheet-conveying element, as viewed in a conveying direction of the sheet material, which comprises detecting an actual position of a leading edge of the sheet material by at least one sensor element disposed on the first sheet-conveying element; by a control unit, making a comparison between a nominal and the actual position of the sheet material; and, if the actual position deviates from the nominal position of the sheet material, causing an actuator to fix the sheet material to the following second sheet-conveying element so as to perform a correction of the position deviation.
In accordance with another mode, the method of the invention includes providing jacket surfaces of sheet-guiding cylinders as the conveying elements, the sheet material extending from the jacket surface of a first sheet-guiding cylinder to a jacket surface of a second sheet-guiding cylinder, as viewed in the travel direction of the sheet material.
In accordance with a further mode, the method of the invention includes registering, by the sensor element, a time offset between a start of the movement of an actuator-operated gripper system and a start of movement of the edge of the sheet material covering the sensor element.
In accordance with an added mode, the method of the invention includes measuring the time offset in degrees of machine angle.
In accordance with an additional mode, the method of the invention includes determining the time offset of the start of movement by a sensor element constructed as an edge sensor.
In accordance with yet another mode, the method of the invention includes determining the time offset of the start of movement by a sensor element constructed as a linear CCD.
In accordance with yet a further mode, the method of the invention includes performing the correction of the position of the sheet material based upon the laws of motion of an actuator-operated gripper system provided on the following second sheet-guiding cylinder, whereon the trailing edge of the sheet material is gripped.
In accordance with yet an added mode, the method of the invention includes coming to a conclusion, if a time offset set in the control unit is exceeded, that the trailing edge of the sheet material has not been gripped by an actuator-operated gripper system.
In accordance with another aspect of the invention, there is provided a device for correcting a position of a sheet material when a direction of motion of the sheet material is reversed in a reversing device, comprising a holding device of a sheet-guiding cylinder serving as a storage drum, a sensor element for sensing a leading edge of the sheet material, the sensor element being assigned to the holding device, another holding device for a trailing edge of the sheet material disposed on a sheet-guiding cylinder serving as a turning drum, and an operatable actuator assigned to the other holding device of the sheet-guiding cylinder serving as the reversing drum for position correction of the other holding device.
In accordance with a first alternative embodiment of the invention, the operatable actuator is constructed as a linear drive.
In accordance with a second alternative embodiment of the invention, the operatable actuator is constructed as a piezoelectric actuator.
In accordance with a third alternative embodiment of the invention, the operatable actuator is constructed as a magnetic bearing.
In accordance with a further feature of the invention, the sensor element and the other holding device of the sheet-guiding cylinder serving as a reversing drum are connected to one another via a control unit with data and control lines, and the control unit has a control device and a characteristic-curve family map wherein parameters relating to the sheet material to be processed are stored.
In accordance with an added aspect of the invention, there is provided a reversing device for sheet material in sheet-processing machines, in combination with a device for correcting a position of sheet material when a direction of motion thereof is reversed, comprising a holding device of a sheet-guiding cylinder serving as a storage drum, a sensor element for sensing a leading edge of the sheet material, the sensor element being assigned to the holding device, another holding device for a trailing edge of the sheet material disposed on a sheet-guiding cylinder serving as a reversing drum, and an operatable actuator assigned to the other holding device of the sheet-guiding cylinder serving as the reversing drum for position correction of the other holding device.
In accordance with an additional aspect of the invention, there is provided a printing unit having a device for correcting a position of sheet material in a reversing device, comprising a holding device of a sheet-guiding cylinder serving as a storage drum, a sensor element for sensing a leading edge of the sheet material, the sensor element being assigned to the holding device, another holding device for a trailing edge of the sheet material disposed on a sheet-guiding cylinder serving as a reversing drum, and an operatable actuator assigned to the other holding device of the sheet-guiding cylinder serving as the reversing drum for position correction of the other holding device.
In accordance with a concomitant aspect of the invention, there is provided a multicolor printing machine for processing sheet material, in combination with a device for correcting a position of a sheet material in a reversing device, comprising a holding device of a sheet-guiding cylinder serving as a storage drum, a sensor element for sensing a leading edge of the sheet material, the sensor element being assigned to the holding device, another holding device for a trailing edge of the sheet material disposed on a sheet-guiding cylinder serving as a reversing drum, and an operatable actuator assigned to the other holding device of the sheet-guiding cylinder serving as the reversing drum for position correction of the other holding device.
The advantages which can be achieved with the invention can primarily be seen in that the determination of the time offset, which can be measured in machine degrees and therefore independently of the speed, can be used to determine the start of the relative movement between the sheet leading edge and the gripper system in relation to the relative movement expected at the sheet trailing edge in accordance with the laws of motion. Therefore, a measure is available for the necessary reversing color register correction on the surface of the sheet-guiding cylinder following a first sheet-guiding cylinder configured, for example, as a storage cylinder. Determining the time offset in machine degrees permits a determination which is independent of the printing speed of the rotary printing machine. On the way to the next printing unit of a sheet-processing multicolor rotary printing machine having a plurality of printing units, a position correction determined in this way can be controlled or regulated out appropriately on one of the sheet-carrying components by an actuator. This means that, for example on the outer surface of a storage drum, a correction can be made to the position of the sheet.
In an advantageous refinement of the concept upon which the invention is based, a time offset between the start of the movement of an actuator-operated gripper system and the start of movement of the edge of the sheet material that covers the sensor element can be registered by the sensor element on an outer cylindrical or jacket surface of a first sheet-guiding cylinder. From the determination of this time offset, a position correction can be achieved in the form of a position correction, performed by a control unit, of the actuator-operated gripper system on the circumference of the cylinder functioning as a storage drum and arranged downline from the first cylinder guiding the sheet material, as viewed in the travel direction of the sheet.
In order to register the time offset independently of the printing speed of the rotary printing machine, the offset is measured in degrees of machine angle. A measurement in degrees of machine angle can be performed particularly simply and with high reliability.
The measurement of the time offset of the start of movement may be performed by a sensor element constructed as an edge sensor. In addition to constructing the sensor element arranged on the jacket surface of the first sheet-carrying cylinder as an edge sensor, it may also be constructed as a linear CCD sensor.
It is equally possible to use sensors which detect light that shines through, from which the presence or the absence of a sheet material in the position thereof on the first sheet-guiding cylinder can be detected.
In order to determine the position correction of the sheet material during the turning operation from the front thereof to the back thereof, which then represents the new front to be printed subsequently, a calculation is performed based upon the laws of motion of the actuator-operated gripper system on the first following sheet-guiding cylinder, functioning as a storage drum, on which the trailing edge of the reversed sheet material is gripped. If a time offset preset in the control unit is exceeded, it is possible to conclude that the trailing edge of the sheet material has not been gripped by the actuator-operated gripper system on the sheet-guiding cylinder which follows the first sheet-guiding cylinder and which serves as a storage drum in a reversing device. Therefore, by determining the time offset, proposed in accordance with the invention, from the start of movement of the sheet leading and sheet trailing edge, it is also possible to make deductions about the presence or the absence of a copy of the sheet material on the jacket surface of sheet-guiding cylinders. This criterion for the detection of missing sheets can be implemented in addition to already known missing-sheet criteria and, in combination with the criterion, can help to reduce the probability of error or can be used as the sole sensor system for monitoring missing sheets.
By the proposed solution according to the invention, a position correction may therefore be made with high precision and high reliability, because the tautening of the sheet material to be turned or reversed can be influenced directly, even during the reversing or turning operation, by the sensor element and the actuator-operated gripper system that grips the new sheet leading edge, i.e., the old sheet trailing edge of the sheet material. By arranging the sensor system that detects the position of one sheet edge on the first sheet-guiding cylinder, and also the provision of the actuator-operated gripper system on the following or succeeding cylinder guiding the sheet material, the element that picks up the new sheet leading edge can be used to correct the position of the sheet material on the circumference of the sheet-guiding cylinder serving, for example, as a storage drum. On the way to the next printing unit, the position correction thus determined may be controlled out appropriately, on one of the sheet-carrying components, by an actuator with which the actuator-operated gripper system is moved.
In an advantageous refinement of the concept upon which the invention is based, the actuator of the actuator-operated gripper system may be constructed as a linear drive. In addition to the construction of the actuator element as a linear drive, the actuator can also be constructed as a piezoelectric actuator; furthermore, the operatable actuator of the gripper system on the following sheet-guiding cylinder serving as a storage drum can be constructed as a magnetic bearing. The sensor element on the first sheet-guiding cylinder and the actuator-operated holding device of the sheet-guiding cylinder arranged downline from the latter and serving as a turning drum are connected to one other via a control unit and via data and control lines, the control unit having both a storage device and a characteristic-curve family, wherein parameters, respectively, relating to the sheet material to be processed are stored. Such parameters can be, for example, the grammage, the format, the quality of the cut edge, the tolerances of these dimensions, and so forth.
A device having the foregoing features may preferably be used on a reversing or turning device belonging to rotary printing machines for processing sheet material. The reversing or turning device is preferably used in multicolor rotary printing machines and is arranged approximately in the middle of the multicolor rotation, for example, after the second printing unit in the case of four printing units with a finishing unit, and after the third printing unit in the case of six printing units with a finishing unit; however, different embodiments are also conceivable wherein the reversing or turning unit is even arranged after the second printing unit. Reversing or turning devices for sheet material are preferably used in multicolor rotary printing machines.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for adjusting the position of sheet material when the direction of motion thereof is reversed, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: